Dexterity analysis of three 6-DOF continuum robots combining concentric tube mechanisms and cable driven mechanisms

Continuum robots are increasingly used in minimally invasive surgeries. To date, concentric tube mechanism and cable driven mechanism have been two prevalent mechanisms for constructing continuum robots. As these two mechanisms complement each other, it is worth exploring the possibility of combining them together. In this paper, we investigate the dexterity of three continuum robots combining both mechanisms. Indices based on the concept of orientability are introduced to analyze the distribution of the dexterity. A Monte Carlo method is used to calculate the dexterity distribution across the workspace. Particularly, directional dexterity indices are put forward to describe the dexterity along different axes. Results imply that evenly allocating degrees of freedom (DOFs) among the segments achieves the best workspace and dexterity. Otherwise, assigning more DOFs to the proximal segment tends to enlarge the workspace and adding more DOFs to the distal segment tends to improve the dexterity. In addition, the dexterity along different axes can vary significantly and thus requires special attention when applying the robot to specific surgical procedures

Design and nonlinear spatial analysis of compliant anti-buckling universal joints

Compliant universal joints have been widely used in many applications such as precision transmission mechanisms and continuum robots. However, their nonlinear spatial analysis in terms of load-displacement relations is less investigated in the compliant mechanisms community, which are needed to show the physical insight into constraint behavior of the universal joint. In addition, the design of existing compliant universal joints is not robust to withstand buckling under applied compression loads. This paper aims to address these problems and starts from presenting a novel anti-buckling universal joint consisting of two inversion-based symmetric cross-spring pivots (IS-CSPs). Two nonlinear spatial models of the IS-CSP and of anti-buckling universal joint are proposed, resorting to two single-sheet closed-form kinetostatic models as the first step, respectively. Then center shifts, primary rotations, and load-dependent stiffness are parametrically studied under different loading conditions over a load and displacement range of practical interest, namely, point loads, cable-force actuations, and varying loading positions. The modeling results of these performance characteristics are shown to be accurate using nonlinear finite element analysis. In addition, preliminary experimental tests are carried out to investigate the manufacturability of the prototype and verify the nonlinear spatial models. Finally, this paper presents and models two new bi-directional anti-buckling universal joints, each with two IS-CSPs and two non-inversion-based symmetric cross-spring pivots (NIS-CSPs)